Quenching of metals



Patented Aug. 24, 1943 2,327,383 our-moo or METALS Cliflord G. zur Horst, Hampton Township, illleghcny countyrBla-lne Wescott, Churchill, and Leslie W. Vollmer, Plttshurg Pa, assignore to G Research a Development lilompany, Pittsburgh, Pa... a aeration oi Delaware No wing. Application January 12, 1942, Se No. ceases (@l. Ett -1t) i3 illaima.

This invention relates to the quenching of metals; and it is particularly. concerned with an improved quenching oil produced by a process comprising incorporating in a mineral quenching oil a petroleum oil propane refining residue in a controlled amount adequate to substantially increase the initial five second quenching speed without substantially modifying the stress reducing characteristics of the oil and it further comprises an improved process of quenching metals wherein the preheamcl metal is quenched by immersion in a, quenching oil loath comprising a mineral quenching oil and at least about (9.5 per cent of a petroleum oil propane refining residue; all as more fully hereinaiterset forth and as claimed.

This invention is useful in the quenching of any metal which is advantageously quenched in an oil bath having a high initial quenching speed, but it is particularly useful in the quenching of iron base alloys and it will he described hereinafter in detail in connection with the quenching of steel.

Many metal alloys, particularly iron base alloys, such as carbon steels and alloy steels, require heat treatment for the development of maximum properties of hardness and strength; These properties are dependent upon the establishment of certain physical structures in the metallic components of the alloy. In steel, hardenability is determined by the extent to which loy. The production of this structure in steel is usually accomplished by arresting at the desired point, the changes in the internal structure of the alloy which take place during the cooling of the steel from high temperatures. The fact tend to set up :rcessive amounts of internal stress in the steel resulting in distortion and warping and, in the extreme case, cracking of the quenched piece. As a result, aqueous quenching media have been supplanted by mineral oil quenching media where such mineral oil quench-= ins media have suficiently high quenching speeds to produce the desired properties in the quenched a martensltic structure is established in the althat these physical changes require time for their completion makes it possible to arrest them at the desired point by suitable quick cooling.

Quenching of the steel in aqueous or oil quenching baths is generally used to arrest these physical changes. It is advantageously carried out in such manner that the physical changes in the steel are arrested at or near the point at which maximum hardness is obtained, and is folv .lowed by a tempering treatment involving heating at relatively low temperatures to impart the desired ductility or toughness to the metal at some sacrifice in hardness.

Quenching in aqueous media develops the properties of strength and hardness to the maximum obtainable for a given section of metal. However, quenching in aqueous quenching media is undesirable in many cases because these media metal, because such mineral oil quenching media are particularly adapted to minimize internal stresses and distortion in the quenched product.

This results from the fact that the quenching speeds of mineral oil quenching media are sub stantially' slower than those of aqueous quenchlng media, due to considerable extent to the formation of a more or less persistent vapor envelop about the quenched piece at the beginning of the quenching cycle, and the fact that in the later stages of the quenching cycle the quenching speeds of mineral oil quenching media are sumclcntly slow so that the internal stresses developed in the metal inthe early stages of the cycle tend to be relieved.

Consequently, the overall cooling efficiency of the mineral oil quenching media heretofore known is not as great as that of aqueous quench ing media and it has been difiicult or impossible to effect in mineral oil quenching baths quenching oi pieces formed of steels having high critical cooling rates, suficiently rapidly to develop the properties of strength and hardness to their maximum values or the quenching of pieces having high mass to surface ratios sumciently rapidly to develop the properties of hardness and strength to the maximum depth.

It is desirable therefore to improve the quenching of metals in mineral oil quenching media so that the cooling efiiciency in the early stages of the quenching cycle is increased to more nearly approach the cooling efiiciency of aqueous quenching media without increasing the quenching speed in the later stages of the cycle sulfioicntly to deleteriously affect the normal stressrelieving properties of the mineral oil.

It is an object achieved by the present invention to provide a method of quenching metals, particularly iron base alloys, in mineral oil quenching media having initial quenching speeds greater than the mineral oil quenching media heretofore known. It is a further object achieved by the present invention to provide a process of producing mineral oil quenching compositions having cooling efficiencies more nearly approaching the cooling efliciency of water while retainquenches, and the compositions obtained thereby.

The critical cooling rate of a metal is defined as the lowest cooling rate at which maximum hardness is developed. For steel the critical cooling rate is the lowest cooling rate which will produce a full martensitic structure in the steel. Thus it is generally most desirable to efiect initial quenching at a speed sufficient to produce a cooling rate at least equal to the critical cooling rate for as greath a depth in the metal as possible and to effect the quenching with a minimum of distortion.

The cooling eiilciency of a quenching speed and the initial five second quenching speed is a convenient measure of the property of quenching oil compositions with which this invention is most concerned. The initial five second quenching speed of a quenching oil composition as referred to throughout this specification and in the appended claims is detennined according to the following formula:

Temperature rise in 5 sec. test Per cent available heat rc- Temperature rlseln cold quench tcst moved in first five seconds in which the respective values are measured as follows:

Cylindrical test pieces one inch in diameter and 2.5 inches long of stainless'steel containing about 18.0 per cent of chromium and 8.0 per cent nickel are heated for one hour at 1500" F. in a furnace equipped with an automatic temperature control. Two quarts of the quenching oil composition to be tested are placed in a calorimeter which has a wire screen positioned in the center of the oil bath to insure constant depth of immersion of the samples. The quenching composition is heated to an initial temperature of 100 F.

One of the preheated test pieces is immersed in the quenching bath by means of light tongs for'a period of five seconds without agitation. The test piece is then removed and the bath agitated and the maximum temperature reachedis measured. A second p eheated test P ce s immersed in the bath at an initial temperature of 100 F. and the bath is agitated until the maximum rise in temperature has been produced.

The maximum temperature rise measured in this cold quench represents the available heat of the test piece. By substituting the value thus determined for the five second quench and for the cOld quench in the above formula a measure of the heat removed in the first five seconds as compared with the total available heat is obtained and is referred to herein as the initial five second quenching speed.

We have discovered that the residues produced in the propane refining of petroleum oils have the property, when incorporated in a light mineral oil such as has heretofore been used in the quenching of metals, .of substantially increasing the initial five second quenching speed of such an oil without lessening its stress reducing characteristics and that by incorporating such petroleum oil propane refining residues in mineral quenching oils in amounts as small as 0.5 per cent by weight, substantial increases in the initial five second quenching peeds of the oils can be produced. Furthermore, we have found that by quenching pieces formed of metals having high critical cooling rates or metal pieces difficult to quench because of a high ratio of mass to surface, by immersion in quenching oil compositions containing such petroleum oil propane refining residues cooling of the metal can be efiected at a rate more nearly approaching or equal to minimum of distortion.

The petroleum oil propane refining residues referred to herein are such as are obtained by the treatment of a parafiinic, mixed base or naphthenic petroleum oil reduced crude such as a topped crude or lubricating oil stock, cylinder stock, a short residuum, or the like with liquid propane to effect separation of asphaltic, waxlike, and resinous hydrocarbon constituents from the parafiinic lubricating oil portion of the stock. Liquid propane is used extensively either alone or in combination with other solvents for the solvent refining of various petroleum stocks and recovery of highly paraffinic lubricating oils from them. Liquid propane under pressure at normal or atmospheric temperature is an excellent solvent for petroleum oil products. Upon raising the temperature of the solution to about F. the asphaltic components of the oil are precipitated out and at somewhat higher temperatures up to 212.5 F., the critical temperature of propane, highly viscous, high molecular weight parafilnic petroleum resins separate out. Such treatment is known in the art as propane deresining and is so designated herein and in the appended claims. When the temperature of a propanepetroleum oil solution is lowered below normal atmospheric temperatures waxy products sepa rate out and may be recovered by filtration. This operationis known in the art and referred to herein and in the appended claims as propane dewaxing. The propane deresining treatment is sometimes combined with treatment with other solvents such as cresylic acid, phenol and the like for separation of aromatic constituents to increase the parafiinicity of the lubricating oil.

All of these propane precipitated products whether obtained by the use of propane alone or the use of propane in conjunction with other solvents such as phenol and cresylic acid, we have found the property of increasing the initial five second quenching speed of a mineral quenching oil and by the term petroleum oil propane refining residues we mean to include all of the propane precipitated products whether they consist predominantly of asphaltic, waxy, or resinous hydrocarbon materials with or without substantial quantities of aromatic constituents,

The various petroleum oil propane refining residues do not increase the initial'five second quenching speed of a mineral oil in the same degree. Some are more eifective than others and are advantageously used'in smaller amounts. We have found also that in most cases the effect of each propane refining residue increases di rectly with the amount used, up to a maximum and then decreases. Consequently the optimum range of concentration for different propane refining residues will differ. In general we have found that amounts of propane refining residue between about 0.5 and 20.0 per cent by Weight 2,sa7,sss

possible therefore by suitably compounding quenching oil compositions according to our invention to provide a quenching medium which has an initial five second quenching speed particularly adapted to give best results with the particular metal and the particular type of piece being quenched. For most purposes it is advantageous to use a quenching composition having an initial five second quenching speed of at least about 30.0 per cent and for this reason we find it most advantageous to use the propane refining residues in amounts corresponding to at least about 1.0 per cent by weight of the oil.

In compounding the quenching oil compositions of our invention we select for the quenching bath a mineral oil of the type customarily used for quenching steel and other metals and these oils are referred to herein as mineral quenching oils. The oils used for this purpose may be either naphthenic .or paraifinic oils and are usually acid treated neutral oils having a viscosity of about '70 to 200 S. U. S. at 100 F., relatively high flash and fire points, and substantial heat stability and resistance to slud ing. For optimum results we have found that paraifinic oils which usually have'an initial five second quenching speed between about 17.0 and about 19.0 per cent are most advantageous.

We have found also that mixtures of the quenching accelerating agents of our invention may be used. However, in such case, the effect of the respective agents may not be entirely additive and the optimum amounts of the respective agents, when used alone, may produce less satisfactory results in mixtures than do somewhat smaller amounts of each agent.

The actual quenching operation using the quenching compositions of our invention is usually carried out by immersion of the preheated metal in the quenching oil composition until suihcient heat has been removed to reduce its temperature the desired. cunt. The quenching oil may be used repeatedly with only slight deterioration.

Among the propane refining residues we have found most suitable for the purposes of our invention are those obtained by the treatment of pare-fin base stoclss with propane alone and those obtained from mixed base stoclrs by treatment with propane in combination with solvent poses oi our invention include both the propane dewazirig residues and the propane deresining residues. The paraifinic petroleum oil propane deresining residues consist predominantly of very high molecular weight parafinic hydrocarbons and theyhave viscosities upwards of 400 S. U. S. at 210 and as high as 5600 S. U. S. at 210 The parafiinic petroleum oil propane deresining residue we have found to be particularly efie'ctive in increasing the quenching speeds of mineral quenching oils. The parafiinic base petroleum oil propane dewaxing residues consist predominantly of amorphous wax. They are also eii'ective' quenching accelerating agents but are somewhat less potent than the parai'fin base petroleum oil deresining residues.

In a. typical process for the production of paraflin petroleum oil propane refining residues contemplated for use according to our invention a Pennsylvania reduced crude is first dissolved in about two volumes of liquid propane under pressure at atmospheric temperature. The solution is then cooled for dewaxing by evaporation of propane to a temperature usually about 0 F. The propane-oil ratio of the solution is maintained substantially constant during this operation by the addition of chilled liquid propane. Wax separates out of the chilled solution and is filtered oil. The residual wax product thus obtained we have found is substantially effective in increasing the initial five second quenching speed of a mineral quenching oil and when incorporated in such an oil in amounts corresponding to about 1.0 to 20.0 per cent produce quenching media having initial five second quenching speeds from about 20.0 to 35.0 per cent.

The solution of dewaxed oil in liquid propane recovered from the dewaxing step of the process is diluted with liquid propane to a proportion of about ten volumes of propane per volume of oil and is heated for deresining to a temperature usually above about 120 F. and less than 212.5

Bill

F'., the critical temperature of propane. Under these conditions a predominantly parafiinic resin product is precipitated. This parafllnic resin residue is separated from the solution by settling and is fractionated to recover products having widely divergent viscositie's. The fractionation is carried out by dissolving the residue in additional propane and passing the solution through a plurality of settlers at progressively increasing temperatures. The product settling out in each settler is pumped separately to a depropanizing still where propane is separated and fractions of the paraffinic petroleum oil propane deresining residue having viscosities between about 400 S. U. S. and 5600 S. U. S. at 210 F. are recovered. These residues vary in appearantce from heavy liquid to semi-solid tarry produc s.

The parafflnic petroleum oil propane dereeinlng residues thus recovered we have found are particularly advantageous for the purpose oi our invention. They are particularly effective in increasing the initial five second quenching speed of a mineral quenching oil and when used even in very small amounts they produce a substantial increase in quenching speed. When used in amounts cotresponding to about 0... to 20.0 per cent by weight of the oil they produce quenching compositions having initial five second quenching speeds between about 20.0 and per cent.

Typical parafinic petroleum oil propane deresining residues obtained by the process above described exhibited the following properties:

Table l!" Resiuous residues Properties A B c 21.4 620 72c 25 818 as 5. 20

Propane refining residues suitable for the purposes of our invention may also be recovered by processes involving the use of other solvent refining agents in conjunction with propane.

' These processes are usually applied to mixed base oils such as a Mid-Continent oil for removal of the aromatic components along with the compounds normally separated by propane refining. In such case the propane refining residue re covered is mixed with a substantial amount aromatics and we have found such mixtures are also particularly effective for increasing the initial five second quenching speed oi a mineral quenching oil. When used in amounts corresponding to 0.5 to 20.0 per cent by weight of the oil they produce quenching compositions having initial flve second quenching speeds between about 20.0 and 39.0 per cent.

A typical product obtained by such a process in which a short residuum of an Oklahoma crude was treated with liquid propane and a cresylic acid solvent, exhibited the following properties:

Table II Resinous residue D Specific gravity fill/60 F 1.041 Flash F 545 Fire F 640 Four F +125 Viscosity S. U. V. 300 F 366 Carbon residue 18.0

In the following examples there are illustrated specifically several of the more advantageous forms of our invention and the results obtainable thereby.

Example I.--A series of quenching oil compositions was prepared by incorporating in a neutral paraffinic mineral quenching oil having a viscosity of 100 S. U. V. at 100 F., various amounts, between 1.0 and 20.0 per cent by weight, of an amorphous wax residue obtained by the propane dewaxing of a steam refined bright stock from a Pennsylvania paraflin base crude. The initial five second quenching speeds of the respective compositions were measured as above described and the following results were obtained:

Initial five second quenching speed Quenching 'nil 16.98 Quenching oil+1.0% waxy propane refining residue 20.75 Quenching oil+2.0% Waxy propane refining residue 22.70 Quenching oil+3.0% waxy propane refining residue; 27.39 Quenching oil+4.0% waxy propane refining residue 29.15

Quenching oil+5.0% waxy propane refining residue" 29.60 Quenching oil+7.5% waxy propane refining residue 33.33 Quenching oil+10.0% waxy propane refining residue Quenching oil+12.5% waxy propane refin- 7 ing residue 33.33 Quenching oil+15.0% waxy propane refining residu Quenching oil+17.5% waxy propane refining residue 35.43 Quenching oil+20.0% waxy propane refining residue 33.46

These results demonstrate that this type of waxy propane refining residue is quite effective in increasing the initial five second quenching speed Quenching n of a propane deresining residue obtained from a,

Pennsylvania paraflin base crude and having the properties shown above in Table I for resinous residue A. The initial five second quenching speeds of the respective compositions were measured as above described and the following results were obtained:

Initial five second quenching speed 16.98 Quenching oil+1.0% resinous propane refining residue A 28.02 Quenching oil+2.0% resinous propane refining residue A. Quenching oil+3.0% resinous propane refining residue A Quenching oi1+4.0% resinous propane refining residue .A 37.32 Quenching oil+5.0% resinous propane refining residue A Quenching oil+7.5% resinous propane refining residue A Quenching.oil+l0.0% resinous propane refining residue A 35.94 Quenching oil+ 12.5% resinous propane refining residue A 35.29 Quenching oil+15.0% resinous propane re- 'fining residue A 34.64

These results demonstrate the fact that this type of propane deresining residue is extremely efiective in increasing the initial five second quenching speed of a mineral oil such as has been used heretofore in the quenching of metals. These results also demonstrate the fact that the increase in quenching speed increases with amount of quenching accelerating agent used up to a maximum and then slowly decreases. Also it will be noted upon comparison of these results with those shown above in Example I that this type of propane deresining residue is substantially more eifective in increasing quenching speed than the propane dewaxing residue shown in Example I when used in corresponding amounts.

Example III.A third series of quenching oil compositions was prepared by incorporating in a neutral paraifinic mineral quenching oil having a viscosity of S. U. V. at 100 F., various amounts between 1.0 and 15.0 per cent by weight, of a propane deresining residue obtained from a Pennsylvania paraifin base crude and having the properties shown above in Table I for resinous residue B. The initial five second quenching speeds of the respective compositions were measured as above described and the following results were obtained:

Initial five second quenching speed Quenching nil 16.98

Initial five second quenching speed Quenching oi1+5.0% resinous propane refining residue B 36.20 Quenching oil 7.5%+ resinous propane refining residue B 35.29 Quenching oil+l0.0% resinous propane refining residue B 35.83 Quenching oil-{42.5% resinous propane refining residue B 34.76

Quenching oil+15.0% resinous propane refining residue B 32.56

These results demonstrate that this type of propane deresining residue is also quite effective in increasing the initial five second quenching speed of a mineral oil such as has been used heretofore in the quenching of metals. These results also show the fact that the increase in quenching speed increases with the amount of quenching accelerating agent used up to the maximum and then decreases. 7

Example IV.A series of quenching oil compositions was made by using as the quenching accelerating agent propane refining residue D obtained by treating a mixed base Mid-Continent short residuum from an Oklahoma crude with liquid propane in combination with cresylic acid and having the properties shown above in Table II. This propane refining residue was incorporated in various amounts between 1.0 and 20.0 per cent by weight in a neutral parafiinic quenching oil having a viscosity of 100 S. U. V. at 100 F. and an initial five secondquenching speed of 16.98 per cent. The resulting compositions had initial five second quenching speeds as follows:

Initial five second quenching speed Quenching oil 16.98 Quenching oil+1.0% propane refining residue D 28.57 Quenching oi1+2.0% propane refining residue D 31.27 Quenching oi1+3.0% propane refining residue D 34.2% Quenching oil+i.0% propane refining residue D 35,56 Quenching oil+5.0% propane refining residue D 36.4w; Quenching oil+7.5% propane refining residue D 38.26 Quenching oi1+l0.0% propane refining res== idue D $8.56 Quenching oil+ 12.5% propane refining residue D 37.9? Quenching oil+l5.0% propane refining residue D 37.89 Quenching oil-{47.5% propane refining residue D 37.63 Quenching oil+20.0% propane refining residue D 37.53

These results demonstrate that a propane extraction residue obtained by the extraction of a mixed base crude with both liquid propane and cresylic acid is particularly efiective in increasing the initial five second quenching speed of a mineral oil such as has been used heretofore in the quenching of metals. The fact that the increase in quenching speed increases with the amount. of quenching accelerating agent used up to a maximum and then decreases is also shown.

While we have described our invention with reference to certain specific embodiments thereof, it is to be understood that this invention is.

not limited to such specific embodiments except as hereinafter defined in the appended claims.

What we claim is: 1. An improved quenching oil composition comprising a mineral quenching oil and at least about 0.5 per cent by Weight of a petroleum oil propane refining residue.

2. An improved quenching oil composition comprising a mineral quenching oil and about 0.5 to 20.0 per cent by weight of a petroleum oil propane refining residue.

3. An improved quenching oil composition comprising a mineral quenching oil and at least about 0.5 per cent by weight of a mixed base petroleum oil propane refining residue.

4. An improved quenching oil composition comprising a mineral quenching oil and at least about 0.5 per cent by weight of a parafiin base petroleum oil propane dewaxing residue.

5. An improved quenching oil composition comprising a mineral quenching oil and at least about 0.5 per cent by weight of a paramnic petro leum oil propane deresining residue.

6. An improved quenching oil composition comprising a mineral quenching oil and a petroleum oil propane refining residue in controlled amount adequate to impart to said quenching oil an ini tial five second quenching speed or at least about 20.0 per cent without substantially modifying the stress reducing characteristics of the oil.

7. An improved quenching oil composition comprising a mineral quenching oil and a mixed base petroleum Oll propane refining residue in controlled amount adequate to impart to said quenching oil an initial five second quenching speed of at least about 20.0 per cent withoutsubstantially modifying the stress reducing characteristics of the oil.

8. An improved quenching oil composition comprising a mineral quenching oil and a parafilnic petroleum oil propane dewaxing residue in controlled amount adequate to impart to said quenching oil an initial five second quenching speed of at least about 20.0 per cent without substantially modifying the stress reducing characteristics of the oil.

9, An improved quenching oil composition comprising a mineral quenching oil and a parafiinic petroleum oil propane deresining residue in controlled amount adequate to impart to said quenching oil an initial five second quenching speed oi at least 20.0 per cent without substantially modifying the stress reducing characteristics of the oil.

10. A method of quenching metals comprising 1 heating the metal to a temperature above its critical temperature and thereafter cooling the metal by immersion in a quenching oil bath comprising a mineral quenching oil and an amount of a petroleum oil propane refining residue, above about 0.5 per cent, adequate to impart to the quenching oil bath an initial five second quenching speed of at, least about 20.0 per cent.

11. A method of quenching metals comprising heating themetal to a temperature above its critical temperature and thereafter cooling the metal by immersion in a quenching oil bath comprising a mineral quenching oil and an amount of a mixed base petroleum oil propane refining residue, above about 0.5 per cent, adequate to impart to the quenching oil bath an initial five second quenching speed of at least about 20.0 per cent.

12. A. method of quenching metals comprising heating the metal to a temperature above its critical temperature and thereafter cooling the metal by immersion in a quenching oil bath comprising a mineral quenching oil and an amount; of a, paraflinic base petroleum oil propane dewaxlng residue, above about 0.5 per cent, adequate to impart to the quenching oil bath an initial five second quenching speed of at least about 20.0 per cent.

13. A method of quenching metals comprising heating the metal to a temperature above its critical temperature and thereafter cooling the metal by immersion in a quenching oil bath comprising a mineral quenching oil and an amount of a. paraflinic base petroleum oil deresining residue, above about 0.5 per cent, adequate to impart to the quenching oil bath an initial five second q n hing speed of at least about 20.0 per cent.

CLIFFORD G. ZUR HORST.

BLAINE B. WESCOI'I'.

LESLIE W. VOLLMER. 

